U.S. Pat. No. 3,805,344 discloses a texturing device wherein a yarn thread to be texturized is fed from a supply spool through a feed device into a fluid jet of a texturing device. The yarn thread guided through the fluid jet is then passed over a tension fork and is wound on a take up spool.
The feed device contains two rollers which are driven at different peripheral speeds, namely a first roller which rotates at a relatively slow speed and a second roller the peripheral speed of which is essentially higher. The yarn thread is guided past both rollers. Idler rollers serve to press the yarn thread optionally either against the first roller of the feed device or to the second roller. In the former case, the yarn thread is fed to the texturing device at relatively low speed. In the latter case, the yarn thread is fed at a substantially increased speed. In order to ensure that the yarn thread can be pressed against the second roller by the respective idler roller only after the idler roller has been lifted from the first roller, the two idler rollers are mounted on a pivotable two-armed lever. This lever is held in its normal position by a spring. In this normal position the yarn thread is pressed against the first roller by one idler roller and the other idler roller is lifted off. The lever is rotated into another position by a solenoid against the action of a spring. In this other position said one idler roller is lifted off from the first roller of the feed device and, instead, the other idler roller presses the yarn thread into contact with the second roller.
In this prior art device, the push-pull control of the idler rollers is achieved mechanically by arranging the two idler rollers on a common pivotable lever.
Furthermore it is known to couple one roller of a feed device through magnet clutches optionally with a slow and a fast drive device (Company brochure "Flammen--und Farb--Effekteinrichtung Modell Fatex zur Luft--Texturier--Maschine Modell AT/AT--GD" of Eltex Textilveredelungs--Maschinen GmbH, Reutlingen (West Germany).
In the prior art devices, the solenoids or magnet clutches, respectively, are controlled by control devices which work with punched cards. After one passage of such a punched card (repeating) the temporal sequence of the control commands are repeated. This can result in the formation of patterns (figuring up) in the woven cloth described in the beginning. Though program disturbances are provided to avoid such figuring up. However this is not always successful, whereby second-class end products are obtained.
The lengths of the fancy twists produced on the yarn are to lie within a certain range and are not to exceed a certain upper limit. On the other hand the feed speed is to be as high as possible, in order to increase the output of the machine. In the prior art, a limit is reached due to the inertia of the moved masses, for example of the pivotable lever of U.S. Pat. No. 3,805,344 mentioned above or of the magnet clutches. With a predetermined maximum length of the fancy twist produced, a maximum feed speed determined by the reaction time of the change-over.
Eventually the possibilities of variation provided by the prior art devices are rather limited.